I think it's a fundamentally bad idea to think of class hierarchies as ontological schemata of real world things. It's like ancient philosophers trying to defi

I think it's a fundamentally bad idea to think of class hierarchies as ontological schemata of real world things. It's like ancient philosophers trying to define the human being. Are we FeatherlessBipeds or RationalAnimals? Who really cares? The Circle/Ellipse quabble is academic because it never mentions the actual domain – for what purpose are we trying to model these entities in the first place? Even in pure geometry, there are many different ways to classify and treat these structures. If you have a generic shape representation, you could just have Circle and Ellipse as different builder functions. If you're mostly just concerned with drawing, then a simple "isCircular" method on the Ellipse object might be what you need. And so on...